Unlicensed radio spectrum such as the industrial, scientific, and medical (ISM) radio bands are used for an increasing number of wireless applications using a variety of standards and protocols. Often, a single device is desired to operate using two or more of these standards and/or protocols in the same radio band. For example, in the 2.4 GHz ISM band a device may access a wireless personal area network (WPAN) using a protocol such as Bluetooth as well as a wireless local area network (WLAN) using a protocol such as one of the IEEE 802.11 or “Wi-Fi” protocols.
WPAN protocols such as Bluetooth are generally designed for cable-replacement applications such as wireless headsets, wireless synchronization of personal digital assistants (PDAs) with computers, wireless peripherals such as printers or keyboards, etc. Most Bluetooth implementations support a range of up to approximately 10 m and speeds of up to 700 Kb/sec for data or isochronous voice transmission. Bluetooth can typically support “piconets” of up to eight active devices, with a maximum of three synchronous-connection-oriented (SCO) links. SCO links are designed to support real-time, isochronous applications such as cordless telephony or headsets. Bluetooth also supports asynchronous connection links (ACLs) that are used to exchange data in non-time-critical applications. The Bluetooth physical (PHY) layer uses frequency-hopping spread spectrum (FHSS) at a rate of 1600 hops/sec and Gaussian frequency shift keying (GFSK) modulation. Bluetooth devices typically transmit at a power level of about 1 mW with a raw data rate of approximately 1 Mb/sec.
WLAN protocols include the IEEE 802.11 and/or Wi-Fi family of standards for wireless networking between computers and/or other devices. WLAN protocols generally provide for longer distances (100 m or more) and higher data rates (e.g., 11 Mb/sec, 54 Mb/sec, or more) than WPAN protocols. WLANs are commonly used for internet access, e-mail, file sharing, etc. Like Ethernet, Wi-Fi supports true multipoint networking with such data types as broadcast, multicast, and unicast packets. The MAC address built into every device allows a virtually unlimited number of devices to be active in a given network. These devices contend for access to the airwaves using a scheme called carrier sense multiple access with collision avoidance (CSMA/CA). The Wi-Fi physical layer uses direct-sequence spread spectrum (DSSS) at four different data rates using a combination of differential binary phase-shift keying (DBPSK) for 1 Mb/sec, differential quaternary phase-shift keying (DQPSK) for 2 Mb/sec, and QPSK/complementary code keying (CCK) for 5.5 and 11 Mb/sec. The RF power level can vary, but is typically between 30 and 100 mW in typical WLAN devices.
WPAN and WLAN are generally complementary rather than competing technologies. In particular, coexistence of Bluetooth and Wi-Fi devices is increasingly desired. Because both technologies occupy the 2.4 GHz frequency band, there is potential for interference between the two technologies. The coexistence of two wireless applications such as Bluetooth and Wi-Fi in the same radio band, but with different channel access protocols, requires particular attention to simultaneous operation of both systems in very close proximity.
If Bluetooth and Wi-Fi operate at the same time in the same place, they will interfere (collide) with each other. Specifically, these systems transmit on overlapping frequencies, creating in-band colored noise for one another. The sidebands of each transmission must also be accounted for. Interference between Bluetooth and Wi-Fi may occur, for example, when a Wi-Fi receiver senses a Bluetooth signal at the same time a Wi-Fi signal is being sent to it or when a Bluetooth receiver senses a Wi-Fi signal at the same time a Bluetooth signal is being sent to it.
One solution is to use a Bluetooth coexistence arbiter (BCA) as a media access control (MAC) layer to perform synchronization between the different protocols, and ensure that bandwidth over the shared spectrum is allocated in a non-concurrent yet fair basis. Such a solution would eliminate any potential conflict and still maintain inherent link performance attributes. FIG. 1 shows an exemplary wireless device 100 with WLAN component 101 and Bluetooth component 102. WLAN component 101 and Bluetooth component 102 generally send media access requests to media access controller 103, which applies arbitration rules to determine whether to allow a media access grant and to provide the protocol components 101 and 102 with access to the antenna system for receiving and/or transmitting.
In some coexistence implementations the BCA may reside in the WLAN subsystem while an external Bluetooth component (which may, for example, comprise a separate logical component of the same integrated circuit device as the BCA and/or the WLAN or may be located on a separate integrated circuit device) communicates via an interface to request medium access. As a result, when the WLAN component enters a WLAN power-save mode, both the WLAN component and the integrated BCA component may enter a sleep or other power saving mode of operation (e.g., by gating one or more clock signals, removing core voltage, etc.) for relatively long intervals (typically 100 ms) between waking periods. When the BCA shares the same clock and power domain as WLAN, the BCA may have a blind period during the WLAN power-save interval and be unaware of any Bluetooth activity. The Bluetooth link may be dropped if Bluetooth is denied media access during the WLAN power-save interval.
One solution to this problem is for the BCA to “force” a media access grant to the Bluetooth component just prior to entering the WLAN power-save mode. This resolves the problem of dropping the Bluetooth link during the WLAN power-save mode. However, upon WLAN wakeup, the BCA may be in an unknown state. If the BCA removes the forced Bluetooth grant, it may disrupt an ongoing Bluetooth activity. If this occurs often, as when the WLAN repeatedly wakes to listen for beacons then returns to sleep mode during the sleep interval, then there will be periodic disruptions to the Bluetooth link.
It may therefore be advantageous to arbitrate grant requests after the arbiter wakes from a sleep state based on media access activity that occurs at or before the time when the arbiter wakes from the sleep state.